Although silicone rubber is characterized by its excellent heat resistance, weather resistance, mold releasability, and the like, it is inferior in breaking strength, water resistance and impermeability to gases as compared with general organic rubber, i.e., synthetic rubbers mainly formed by carbon.
In an attempt of obtaining a rubber composition having excellent characteristics of silicone rubber combined with those of organic rubber, various studies on mixtures of these two types of rubber have hitherto been made. For example, it has been proposed to mechanically mix the both as disclosed in Japanese Patent Publication (Kokai) Nos. 41957/79, 139604/80, and 76444/81, or to bond a polyorganosiloxane to carbon-carbon double bonds of an organic rubber as disclosed in Japanese Patent Publication (Kokai) No. 157149/79, Japanese Patent Publication (Kokoku) No. 15497/80, and Japanese Patent Publication (Kokai) No. 31817/80, 76440/81, and 76441/81.
It is actually difficult, however, to mix a silicone rubber and an organic rubber, particularly oil-resistant organic rubber having a polar group, to obtain a uniform mixture due to poor compatibility therebetween.
Moreover, a blend of components that are not co-vulcanizable with each other fails to attain satisfactory physical properties by vulcanization. Thus, none of the conventional proposals to combine silicone rubber and organic rubber has succeeded to bring out the characteristics inherently possessed by each of them.